A polyacetal resin has excellently balanced properties including mechanical strength such as bending elastic modulus and tensile fracture stress, chemical resistance, sliding property and wear resistance, and is easily processed. Because of this, the polyacetal resin is used as a typical engineering plastic widely used in parts such as machinery parts of electrical equipment and automotive parts.
In particular, for automobile parts requiring durability, a polyacetal resin composition reinforced with an inorganic filler is used. The “durability” means long fracture lifetime, for example, under a predetermined stress, and, in other words, creep resistance.
In the polyacetal resin composition reinforced with an inorganic filler in order to improve durability, the polyacetal resin is polymerized and the terminal group of the polyacetal resin is controlled.
Patent Literature 1 discloses a polyacetal resin composition containing a polyacetal resin and a fibrous inorganic filler for improving creep resistance. Patent Literature 1 also discloses that as the molecular weight of a polyacetal resin increases, creep resistance is improved.
Patent Literature 2 discloses a method involving using a plurality of polyacetal resins having different contents of a terminal hydroxyl group in combination in a polyacetal resin composition containing a glass inorganicfiller and a polyacetal resin, to improve interface adhesion between the glass inorganicfiller and the polyacetal resin.
Patent Literature 3 discloses that adhesion to e.g., a glass fiber is improved by using ABA type block copolymer containing a polyacetal skeleton.
Also, as the industrial field of a polyacetal resin is enlarged, it has been desired to improve wear resistance. In an attempt to improve wear resistance, it has been investigated to add an ultrahigh molecular weight polyethylene to a resin composition.
Patent Literature 4 discloses that a lubricant is added in order to improve the wear resistance of a polyacetal resin composition containing a glass fiber. Patent Literature 4 also discloses that an ultrahigh molecular weight polyethylene is preferable as a lubricant.
Patent Literature 5 discloses that a tribology modifier is added to a polyacetal resin composition containing a glass fiber in order to improve mechanical strength, wear resistance and sliding property. In particular, the literature discloses that an ultrahigh molecular weight polyethylene having an average molecular weight beyond 1.0×106 g/mole is preferable as a tribology modifier.